Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F3/00—Brightening metals by chemical means
  • C23F3/04—Heavy metals
  • C23F3/06—Heavy metals with acidic solutions

Definitions

• the present invention relates to the composition of baths for chemical polishing of stainless steel surfaces.
• Chemical polishing of metal surfaces is a technique which is well known (Polissage electrolytique et chimique des metaux Electrolytic and chemical polishing of metals!--W. J. Mc G. Tegart--Dunod--1960 --p.122 et seq.); it consists in treating the metal surfaces to be polished with oxidizing baths. Baths including a mixture, in aqueous solution, of hydrochloric, phosphoric and nitric acids are generally employed for chemical polishing of stainless steels. To improve the quality of the polish it is usual to incorporate suitable additives in these baths, such as surface-active agents, viscosity regulators and brighteners. Thus, U.S. Pat. No.
• 3,709,824 describes a composition of a bath for chemical polishing of stainless steel surfaces, including, in aqueous solution, a mixture of hydrochloric acid, of nitric acid and of phosphoric acid, a surfactant and sulphosalicylic acid as brightener.
• the invention aims to provide polishing baths without phosphoric acid which are designed for carrying out slow and efficacious chemical polishing of stainless steel surfaces.
• the invention relates to phosphoric acid-free baths for chemical polishing of stainless steel surfaces, including, in aqueous solution, a mixture of hydrochloric acid and of nitric acid, an optionally substituted hydroxybenzoic acid and a cationic surfactant, these baths being characterized in that they include, in aqueous solution, ferricyanide complex ions.
• the hydroxybenzoic acid acts as a brightener.
• the hydroxybenzoic acid may be unsubstituted, such as salicylic acid, or substituted, such as 5-sulphosalicylic acid or aminosalicylic acid. Salicylic acid and 5-sulphosalicylic acid are preferred.
• the cationic surfactant advantageously includes a quaternary ammonium salt.
• the quaternary ammonium salt is preferably selected from those which include at least one linear or branched, long-chain alkyl radical. Where appropriate it is preferred to select the quaternary ammonium salt from those in which the long-chain alkyl group contains at least 8 carbon atoms, preferably at least 10 carbon atoms, such as, for example, the lauryl, cetyl and stearyl groups.
• at least one other linear or branched alkyl radical or a substituted or unsubstituted benzyl radical may be present.
• Quaternary ammonium salts which are especially recommended belong to the class formed by the water-soluble alkylpyridinium, especially cetylpyridinium and laurylpyridinium, salts.
• the quaternary ammonium salts including a long-chain alkyl radical as defined above are preferably selected from the halides, in particular the chlorides.
• Alkylpyridinium chlorides are particularly preferred, especially laurylpyridinium chloride.
• Quaternary ammonium salts that can be employed in the baths according to the invention are available among the products of the Dehyquart® trademark (Henkel).
• ferricyanide complex ions are complex cyanides of general formula Fe III (CN) 6 ! 3- , also called hexacyanoferrates (III). They may be present in the aqueous solution in the form of any dissolved compounds such as, for example, hexacyanoferric (III) acid, ammonium ferricyanide, and alkali and alkaline-earth metal ferricyanides. Preferred compounds are alkali metal ferricyanides, potassium ferricyanide being especially preferred.
• the respective contents of hydrochloric, nitric and hydroxybenzoic acids, of cationic surfactant and of ferricyanide complex ions are chosen as a function of the grade of the stainless steel subjected to the polishing and of the polishing conditions, especially of the profile of the steel article subjected to the polishing, of its volume, of the volume of the bath, of its temperature and of the agitation to which it is optionally subjected. They must consequently be determined in each particular case by routine laboratory tests.
• the hydrochloric acid content of the aqueous solution is advantageously at least 1, preferably 2, moles per liter and generally does not exceed 6, preferably 5, moles per liter.
• the nitric acid content is advantageously at least 0.001, preferably 0.005, moles per liter of the aqueous solution and generally does not exceed 0.3, preferably 0.03, moles per liter of the aqueous solution.
• the hydroxybenzoic acid content is advantageously at least 0.1, preferably 1, mg per liter of the aqueous solution and generally does not exceed 15,000, preferably 7000, mg per liter of the aqueous solution.
• the cationic surfactant content is advantageously at least 0.1, preferably 1, mg per liter of aqueous solution and generally does not exceed 1000, preferably 100, mg per liter of aqueous solution.
• the ferricyanide complex ion content in the chemical polishing baths according to the invention is preferably at least 1 ⁇ 10 -7 mole per liter of aqueous solution and, particularly preferably, the ferricyanide complex ion content is at least 1 ⁇ 10 -5 mole per liter. A content of at least 3 ⁇ 10 -5 mole per liter is very particularly preferred.
• the ferricyanide complex ion content preferably does not exceed 1 mole per liter and, particularly preferably, the ferricyanide complex ion content does not exceed 1 ⁇ 10 -3 mole per liter. A content which does not exceed 3 ⁇ 10 -4 mole per liter is very particularly preferred.
• Baths in accordance with the invention which are suitable for ensuring the chemical polishing of surfaces made of chromium- and nickel-alloyed austenitic stainless steel, over a period which varies from 1 to 24 hours and at a temperature of between 20° and 80° C. are those in which the aqueous solution includes, per liter,
• the latter contain, in the aqueous solution, an additive capable of decomposing nitrous acid.
• the function of this additive is to decompose at least a proportion of the nitrous acid which is formed during the polishing of a steel surface, as a result of an oxidation of ferrous ions released in the bath during the polishing.
• the additive capable of decomposing nitrous acid is preferably selected from urea and its derivatives, such as thiourea and urea homologues.
• the optimum content of additive capable of decomposing nitrous acid is from 0.01 to 5 g per liter of the aqueous solution.
• the baths in accordance with this embodiment of the invention are especially suited to the polishing treatments in which the ratio of the surface in contact with the bath to the volume of the latter is higher than 10 m -1 .
• the baths according to the invention may optionally contain additives which are usually present in baths for chemical polishing of metals, for example surface-active agents other than the cationic surfactant defined above, alcohols and viscosity regulators.
• additives which are usually present in baths for chemical polishing of metals, for example surface-active agents other than the cationic surfactant defined above, alcohols and viscosity regulators.
• the baths according to the invention may in addition contain other inorganic acids commonly present in the chemical polishing baths, for example sulphuric acid. They are, however, essentially free from phosphoric acid and phosphate ions.
• the baths according to the invention are suitable for the chemical polishing of stainless steel surfaces. They are well suited to the polishing of austenitic steels containing between 16 and 26% by weight of chromium and between 6 and 22% by weight of nickel, such as steels of 18/8 and 18/10 grades.
• the baths according to the invention are especially well suited to the polishing of austenitic steels containing molybdenum.
• the austenitic steels, with or without molybdenum are typically AISI steels 304, 304L, 316, 316L, 904 and 904L.
• a special feature of the baths according to the invention is that they effect the polishing of such steels at a slow speed.
• a special feature of the baths according to the invention is that they permit slow polishing, and this makes them suitable for the polishing of large industrial pieces of equipment.
• the baths according to the invention have the additional advantage of effecting good quality polishing of assemblies which are welded according to the rules of the art.
• the invention consequently also relates to a process for polishing a stainless steel surface, according to which the surface is placed in contact with a chemical polishing bath in accordance with the invention.
• the metal surface can be brought into contact with the bath in any suitable manner, for example by immersion.
• the time of contact of the surface to be polished with the bath must be sufficient to produce an efficacious polishing of the surface. However, it must not exceed a critical value beyond which the bath loses its polishing properties.
• the optimum contact time depends on many parameters, such as the steel grade, the configuration and the initial roughness of the surface to be polished, the composition of the bath, the working temperature, the agitation of the bath in contact with the surface and the ratio of the area of the surface to be polished to the volume of the bath; it must be determined in each individual case by routine laboratory work.
• the time of contact of the surface to be polished with the bath is, in general, at least one hour, preferably at least two hours.
• the time of contact generally does not exceed 24 hours and preferably does not exceed 12 hours.
• the temperature at which the bath is used is generally lower than its boiling temperature.
• the temperature of use is preferably lower than 80° C. Good results are obtained at a temperature which is lower than or equal to 70° C.
• the temperature of use of the bath is in general at least equal to the ambient temperature. The temperature is preferably at least 35° C.
• the bath is used, at normal atmospheric pressure, at a temperature of 35° to 70° C. and the surface to be polished is kept in contact with the bath for a period of between 2 and 12 hours.
• Example 1 (in accordance with the invention).
• a plate made of austenitic stainless steel of the AISI 316 type was immersed in a polishing bath in accordance with the invention, including, per liter:
• a plate made of austenitic stainless steel of the AISI 904L type was immersed in a polishing bath in accordance with the invention, including, per liter:
• a plate made of austenitic stainless steel of the AISI 316 type was immersed in a polishing bath, including, per liter:
• the bath used consequently differs from the bath of Example 1 in the absence of potassium ferricyanide.
• Example 1 A comparison of the results obtained in Example 1 (in accordance with the invention) with those obtained in Example 3 (not in accordance with the invention) reveals the progress brought by the invention, insofar as the roughness and the brightness which are obtained after the polishing are concerned.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• ing And Chemical Polishing (AREA)
• Chemical Treatment Of Metals (AREA)

Applications Claiming Priority (3)

Publications (1)

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Citations (8)

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• 1994
  • 1994-03-28 FR FR9403732A patent/FR2717829B1/fr not_active Expired - Fee Related
• 1995
  • 1995-03-11 TW TW084102328A patent/TW311942B/zh active
  • 1995-03-13 CA CA002186401A patent/CA2186401A1/fr not_active Abandoned
  • 1995-03-13 US US08/702,435 patent/US5762819A/en not_active Expired - Fee Related
  • 1995-03-13 DE DE69524072T patent/DE69524072T2/de not_active Expired - Fee Related
  • 1995-03-13 CZ CZ962857A patent/CZ285932B6/cs not_active IP Right Cessation
  • 1995-03-13 ES ES95913105T patent/ES2168360T3/es not_active Expired - Lifetime
  • 1995-03-13 PL PL95316536A patent/PL316536A1/xx unknown
  • 1995-03-13 ZA ZA952067A patent/ZA952067B/xx unknown
  • 1995-03-13 HU HU9602669A patent/HU214367B/hu not_active IP Right Cessation
  • 1995-03-13 SK SK1282-96A patent/SK281732B6/sk unknown
  • 1995-03-13 CN CN95193129A patent/CN1044264C/zh not_active Expired - Fee Related
  • 1995-03-13 JP JP7524929A patent/JPH10500732A/ja active Pending
  • 1995-03-13 BR BR9507264A patent/BR9507264A/pt not_active Application Discontinuation
  • 1995-03-13 UA UA96093741A patent/UA48129C2/ru unknown
  • 1995-03-13 AU AU20702/95A patent/AU2070295A/en not_active Abandoned
  • 1995-03-13 PT PT95913105T patent/PT753083E/pt unknown
  • 1995-03-13 WO PCT/EP1995/000942 patent/WO1995026428A1/fr active IP Right Grant
  • 1995-03-13 EP EP95913105A patent/EP0753083B1/fr not_active Expired - Lifetime
  • 1995-03-13 IL IL11296695A patent/IL112966A0/xx not_active IP Right Cessation
  • 1995-03-27 YU YU19895A patent/YU48903B/sh unknown
  • 1995-03-28 HR HR950163A patent/HRP950163B1/xx not_active IP Right Cessation
• 1996
  • 1996-03-13 RU RU96119757A patent/RU2124577C1/ru active
  • 1996-09-24 BG BG100865A patent/BG62338B1/bg unknown
  • 1996-09-27 NO NO964114A patent/NO964114L/no not_active Application Discontinuation
  • 1996-09-27 FI FI963894A patent/FI963894A/fi unknown

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